Humans and other mammalian species are prone to diseases or injuries that require tissue repair or regeneration. For example, treatment of fractures would be improved by new treatment regimens that could stimulate the natural bone repair mechanisms, thereby reducing the time required for the fractured bone to heal. In another example, individuals afflicted with systemic bone disorders, such as osteoporosis, would benefit from treatment regimens that would result in systemic formation of new bone. Such treatment regimens would reduce the incidence of fractures arising from the loss of bone mass that is a characteristic of this disease.
In addition to diseases of the bone, soft tissue diseases, such as intervertebral disc degeneration, may be relieved or reversed by new tissue generation. Disc degeneration is associated with a progressive loss of proteoglycan matrix. This makes the disc more susceptible to further injury and causes low back pain and disc herniations. A person suffering from this condition would benefit from treatment regimen that would induce cells to increase the formation of proteoglycan cartilage.
For at least these reasons, extracellular factors have been investigated for the purpose of using them to stimulate production of new bone, proteoglycan matrix or any other tissues in need of repair. Despite the early successes achieved with extracellular signaling molecules, their use entails a number of disadvantages. For example, relatively large doses of purified extracellular proteins may be required to enhance the production of new bone, thereby increasing the expense of such treatment methods. Furthermore, they are also susceptible to degradation following their introduction into a host animal. In addition, because they are typically immunogenic, the possibility of stimulating an immune response to the administered proteins is ever present.
Due to such concerns, it would be desirable to have available treatment regimens that use intracellular signaling molecules to induce new tissue formation or regeneration.